Artificial pulp grinding stone and method of making same



$2 I V I 2,134,738 S Referfinc? 63mb ROOM PIP-8109 Ndv. 1, 1938. 2,134,738

ARTIFICIAL PULP GRINDING STONE AND'METHOD OF MAKING SAME H. P. SCHEEL, JR

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mmvro ATTORNEY Patented Nov. 1, 1938 PATENT OFFICE ARTIFICIAL PULP GRINDING STONE AND METHOD OF MAKING SAltIE Hans P. Scheel, Jr., Sedro Woolley, Wash.

" Application October 12, 1936, Serial No. 105,284

Renewed January 17, 1938 8 Claims. (Cl. 51 2 06) This invention relates to artificial stones for the grinding of wood pulp and to the method of making artificial pulp grinding stones of the general type disclosed in U. S. Patent No.

1,884,279, issued October'25, 1932, to Hans P.

Scheel and myself.

Pulp grinding stones of this type are of relatively large size and are operated at relatively high speeds and pressures, so that they develop considerable heat in operation. When these stones are made from especially prepared reinforced concrete I find that expansion and contraction, caused by heat generated in the operation of the stone is liable to crack the stone in such a manner as to seriously damage it or entirely destroy its utility.

It is a primary object of this invention to provide a satisfactory reinforcing means and to provide a method of cracking these reinforced concrete pulp grinding stones in predetermined locations, in such a manner that the cracks so formed will be narrow and will be spaced apart and will not damage the stone but will serve as expansion cracks and prevent the formation of other large cracks and cracks which might seriously damage the stone or render the same useless for the purpose of grinding pulp. H

It is a more specific object of this invention to predetermine the location of cracks to be formed in amolded concrete pulp grinding stone by embedding within said stone, at the time it is molded, certain bodies'of material having a higher" coeflicient of expansion than the concrete stone, whereby when the temperature of the pulp grinding stone is substantially raised in the operation of grinding pulp several narrow expansion cracks will be formed at predetermined locations, thereby preventing further cracking of the stone.

In the manufacture of grinding wheels of this type the wheels are necessarily made from cement and relatively fine sharp grit as pulverized quartz or other silicious material. The plastic material is placed in a mold and rotated at high velocity which results in a very solid packing of the material in the peripheral portion of the grinding wheel. With the cements which were formerly available the grinding wheels of this type developed internal chemical heat in setting and curing and it was found desirable to provide temperature controlling means as formed by the pipes in prior Patent No. 1,384,279, hereinbefore referred to. The pipes shown in this prior. patent were ordinary pipes and were designecLto providecooiing means to prevent heating, i.-'.e.,,.to provide. means to admit air iqkeenthewheeimol its manufacture and were designed to positively prevent the formation of checks and cracks. These said pipes were not of enough mass, i. e., heavy enough to produce cracks in the cement in which they were embedded. Low temperature cements are now available which do not develop excessive chemical heat in setting and with these low temperature cements the temperature control pipes shown in the prior patent, hereinbefore identified, may be dispensed with. However, it now develops that under the present very high velocities and pressures to which such grinders are submitted, that provision must be made against uncontrolled checking or cracking occurring as the result of heat developed during normal operation. Accordingly, it is important however that, in wheels made with these low temperature cements, means be provided for predetermining the location and size of the cracks to be formed to insure that the wheels will not be damaged and rendered useless by such cracking due to heat developed by operatio The above mentioned general objects of my invention, together with others inherent in the same, are obtained by the device illustrated in the following drawing, the same being preferred exemplary forms of embodiment of my invention, throughout which drawing like reference numerals indicate like parts.

r In the accompanying drawing Figure 1 is a sectional view of an artificial pulp grinding stone constructed in accordance with this invention, taken in a plane at substantially right angles to the axis of the stone;

Fig. 2 is a sectional view of the same taken in a plane passing through the axis of said stone, as indicated by broken line 2-2 of Figure l; and

Figs. 3, 4 and 5 are fragmentary sectional views illustrating three different modified forms of the invention.

Referring to the drawing, 6 designates a wood pulp grinding stone made from an especially.prepared concrete to provide a fast cutting, eflicient and durable peripheral surface for the grinding of wood pulp. Grinding stones of this type are relatively large, being usually fifty-seven inches or more in diameter and twenty-seven inches or more in width. When these stones are in service in the grinding of wood pulp the normal operating temperature of the stones will range from one hundred thirty to one hundred eighty degrees Fahrenheit, and in case the stones are neglected (as for example permitted to run dry) this temperature may rise as high as six hundred degrees Fahrenheit- Under even the normal operating 5i. ABRADING.

temperatures, these large grinding stones, when molded integrally from specially prepared concrete, will develop internal strains and will crack. Unless some method is provided for controlling this cracking, the cracks which are formed may be so large as to seriously damage the stone, or they may seriously weaken the stone, or they may cause pieces of the stone to break loose from the grinding face, thus rendering the stone totally unfit for use.

In accordance with my invention, I imbed in the stone, when being formed and plastic, a plurality of transverse bars I of metal, as iron, having a higher coefficient of expansion than the concrete from which thestone is made. These bars 1 are placed at a substantial distance inwardly from the periphery of the stone and are spaced'at intervals around the stone. Also reinforcing means are provided embedded in the stone. Preferably the reinforcing means are provided between the bars 1 and the periphery of the stone and also around the bars 1 to provide binding or reinforcing means across any crack which may radiate from the bars 1. While the forms of these reinforcing means may be varied, I prefer to provide a plurality of sets such as 3, (see Fig. 2) of reinforcing bars '8, 9 and I (see also Fig. 1). By having reinforcing means surrounding the transverse bars 1, any crack which radiates from the bars I must traverse a reinforcing bar and such reinforcing means will therefore provide binding means across any such cracks.

I have shown the bars I in Figures 1 and 2 to be in form of iron tubes with heavy solid walls. 0r-

dinary iron pipes can not be successfully used for.

this purpose as they are not heavy enough to crack the concrete when subjected to the changes of temperature to whichthese grinding stones I are subjected. I prefer to use the tubular bars '1 shown in Figures 1 and 2 because the holes in these bars can be utilized to advantage to pass tie rods through at the time the grinding stone is being molded. However, in so far as the forming of the cracks is concerned, I can use bars of substantially any cross sectional shape as long as the mass of metal in the bar is great enough and solid enough to provide the necessary expansion to produce the crack. As illustrative of different shapes of bars which may be successfully used I have shown in Figure 3 a bar II of solid round cross section.--

In Fig. 4 I have shown a bar I2of square cross section. In Fig. 5 I have shown a bar I3 of rectangular cross section. Various other cross sectional shapes may beused.

Grinding stones having iron bars embedded therein, as above described, ordinarily will not crack before use. When these stones are placed in service and become heated the iron bars, as I, I I, I2 or I3 will expand more than the surrounding concrete and narrow cracks M will be formed usually extending from the bars to the periphery 'of the stone. These cracks will be narrow as they Reference These cracks will not weaken the thereof, the above setting forth only preferred forms of embodiment.

I claim: I

1. The method of providing, in a molded concrete pulp grinding wheel, a plurality of substanam!) boom tially radial cracks terminating at the periphery of the wheel, comprising embedding in said wheel, when plastic, at a substantial distance inwardly from the periphery thereof a plurality of transverse spaced apart bars each having a higher coefllcient of expansion than the concrete of which the wheel is made and of a cross sectional area suflicient to crack the wheel from the bars radially outward when the wheel is subjected to a substantial rise of temperature resulting from normal operation.

2. The method of providing expansion cracks at predetermined locations in a reinforced concrete pulp grinding wheel, comprising embedding within said wheel, when plastic, at a substantial distance inwardly from the periphery thereof a plurality of transverse bar members of material having a higher coefficient of expansion than the concrete of which the wheel is made and of a cross sectional areasufficient to crack the concrete wheel in response to a substantial rise of temperature, and embedding reinforcing means surrounding said transverse bars.

3. A reinforced concrete pulp grinding wheel having a plurality of substantially non-compressible transverse metal bars embedded therein, the coeflicient of expansion of said bars being greater than the coefllcient of expansion of the concrete pulp grinding wheel and the mass of said bars being relatively large, whereby expansion of the bars will produce expansion cracks at predetermined locations in the wheel and obviate undesirable cracking of the wheel when the wheel is subjected to a substantial rise in temperature encountered during normal operation.

4. A device of the class described, comprising silicious material bound together by cement to provide a grinding wheel; elements of substantial cross sectional area embedded in said grinding wheel, said elements being expandible in response to heat and being disposed in spaced relation to each other, whereby radial checking of the grinding wheel in response to heat developed during operation occurs in predetermined locations; and reinforcing means surrounding said elements and embedded insaid grinding wheel.

5. A device of the class described, comprising silicious material bound together by cement to provide a grinding wheel; elements of substantial cross sectional area embedded in said grinding wheel, said elements being expandible in response to heat and, being disposed in spaced relation to each other, whereby radial checking of the grinding wheel in response to heat developed during operation occurs in predetermined locations; and reinforcing means embedded in said grinding wheel and extending between'said elements and the periphery of said grinding wheel.

6. The method of providing cracks in predetermined locations in a pulp grinding wheel which is molded out of plastic concrete, comprising embedding in said concrete pulp grinding wheel, when plastic, bodies of iron in a substantially circular path below the surface of the stone, said bodies of iron being of sufficient mass toexpand in response to a substantial rise of temperature resulting from normal operation to provide a plurality of cracks in the grinding stone emanating from said bodies of iron.

'7. The method of providing cracks in predetermined locations in a pulp grinding wheel which is molded out of plastic concrete, comprising embedding in said concrete pulp grinding wheel, when plastic, bodies of material having a higher coefilcient of expansion than concrete in a substantially circular path below the surface of the stone,'said bodies of material being of suflicient mass to expand in response to a substantial rise of temperature resulting from normal operation to provide a plurality of cracks in the grinding stone emanating from said bodies of material.

8. The method of providing cracks in predetermined locations in a pulp grinding wheel which is molded out of plastic concrete, comprising embedding in said concrete pulp grinding wheel, when plastic, transverse bar members 1 having a higher coefllcient of expansion than concrete in a substantially circular path below the surface of the stone, said transverse bar members having a cross sectional area sufflcient to expand in response to a substantial rise of temperature resulting from normal operation to provide a. plurality of cracks in the grinding stone emanating from said transverse bar members.

HANS P. SCHEEL. Jn. 

